Radio receiving system



Dec. 24, 1929. R. E. LACAULT 1,740,946

RADIO RECEIVING SYSTEM Filed April 29, 1924 3 Sheets-Sheet l I I QI I I I I I T f s I yq S 9 OSCILLA TOR ODULA TO o 01 ROUND L RCCCIVEI? Y ;J g; AMPLIFIER INVENTOR ROBE/T C. LA C/IULT BYj M ATTORNEY MICROPHONE TK/HY Dec. 24, 1929. R. E. LACAULT amo nscmvm sYs'rEu Filed April 29, 1924 3 Sheets-Sheet 2 INVENTOR )FOBEKT E. LA CA U LT ATTORNEY Dec. 24, 1929. R. E. LACAULT RADIO nncmivme SYSTEM Filed April 29, 1924 5 Sheets-Sheet 3 R C H 3 B m M. M 35: W H m R M m By m w Patented Dec. 24, 1929 UNITED STATES PATENT OFFICE ROEER'T E. LACAULT, OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, T0 RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE RADIO RECEIVING SYSTEM Application filed April 29,

. The radio receiving system hereinafter described and embodying my invention is an improvement upon the ordinary system employed to receive radio telegraph and radio telephone signals. It is well known that an ordinary vacuum tube of the three electrode type composed of aiilament, a grid and a plate has internal resistance which varies with the electron emission of the hot filament, with the high voltage applied to the plate, and with the potential of the third electrode or grid. In my method of radio reception the important feature resides in the employment of the internal resistance or impedance of a vacuum tube as a variable resistance in the circuit, and the making use of the platefilament resistance in the reception of the signals. The system of radio reception hereinafter described I have called the modulation system and for this reason the vacuum tube acting as a variable resistance I have for purposes of convenience termed the modulator tube.

My invention is of especial importance as regards the super-heterodyne receiving system to which it is particularly applicable, although not limited thereto. In the ordinary type embodying such system the first tube which is provided with a grid leak and condenser and is employed as a frequency changer, serves as a detector with a grid condenser and a grid leak. This first detector rectifies the incoming signal after it has been interfered with by the local oscillations produced by the oscillator tube, and the resultant variations of plate current are amplified through the long wave radio frequency amplifier and detected to make them audible. In this method the amount of energy induced into the tuning circuit is generally regulated by means of a variable coupling between the oscillator and the tuning circuit. This extra control must be adjusted when tuning and as there is a minimum amount of energy to which the detector will respond, such system is necessarily far less efficient especially on weak signals than my improved system as herein described.

In my invention an entirely different principle is used to produce the beats, which are 1924. Serial No. 709,735.

amplified through the long wave radio frequency amplifier and cause the incoming signal to modulate the oscillations produced locally in the same way that the speech and music modulates the carrier wave of a broadcast station. This is a departure from the detector arrangement and is not only more simple than such arrangement, but produces a greater signal strength, which is more noticeable on weak signals. This is due to the fact that my improved system provides greater rectification, no matter how weak the received signal is.

Everyone, who has operated an ordinary regenerative receiver, has noticed that when a broadcast station is being received, a whistle is heard in the telephones when regeneration is increased beyond a certain limit. This is caused by the receiver itself, which oscillates and produces, by interference with the carrier wave of the transmitting station, a beat note of an audible frequency. Such beat note as is well known has a frequency equal to the difference between the two frequencies which produce it. For instance, if a carrier wave of 1,000,000 cycles is received, a beat note of 1,000 cycles will be heard in the receivers if an alternating current of 999,000 cycles or 1,001,000 cycles is made to interfere with it.

In the super-heterodyne receiver, this principle is employed, but instead of producing beat notes at an audible frequency, beats of a super-audible frequency, such for example as 50,000 or 100,000 cycles are generated. The oscillator circuit is tuned by means of a variable condenser, so that such a beat note of predetermined frequency is produced for any incoming signal. Therefore, no matter what the frequency of an incoming signal is, it is always amplified and detected at the same frequency. This is a great advantage because it is easier to design a radio frequency amplifier to function on one frequency only, than one which amplifies in the same proportion over a broad band of frequencies.

In most short wave radio frequency amplifiers, using untuned transformers, the amplification varies for each frequency. It is generally found that greater amplification is obtained at one or two points, while comparatively less amplification is had over the remainder of the frequency range covered by the transformer. If tuned radio frequency transformers are employed, the tuning becomes very complicated, owing to the numerous controls, and it is difficult to tune in a station unless the entire amplifier is calibrated. The radio frequency amplifier used in the super-heterodyne receiver is designed to amplify at maximum intensity at one frequency only, thus increasing the selectivity, since only signal frequencies which are interfered with by means of the oscillator can pass through the amplifier.

Referring to the drawing in which similar characters of designation refer to similar partsthroughout the several views,Figure 1 is a schematic view showing the carrier wave transmitted from a broadcasting station to a receiving station when unmodulated by audible signals impressed thereon by a microphone and Fig. 2 is a similar view show ing a similar carrier wave as modulated by such signals; Fig. 3 illustrates one of the circuits or arrangements of apparatus cmbodying my improved method of radio reception; Figs. 4 and 5 illustrate the general arrangement shown in Fig. 3, a variable resistance being substituted for the modulator; Fig. 6 illustrates a modification of Fig. 3 and the employment of a grid condenser in the circuit; Figs. 7 and 8 illustrate a further arrangement of circuits embodying'my invention ;'Fig. 9 is a diagrammatic view of a superhet erody ne circuit embodying my invention and Fig. 10 is a detail view of the circuit diagrammatically shown in Fig. 9.

My invention maybe compared in its simplest aspects to a combined broadcasting and receiving station such as is diagrammatically illustrated in Figs. 1 and 2. In the former figure is illustrated the character of the oscillations in an undamped carrier wave emitted from the aerial of the transmitting or broadcasting station, when no audible signals from an external source are being impressed upon the microphone at such station. As is shown, such oscillations are continuous and of even amplitude. As is well known when signals are impressed uponthe transmitter through the microphone, as for example, when one speaks into the mouth-piece of the microphone, the carrier wave is modulated and the oscillations thereof vary in amplitude, as illustrated in Fig. 2. Similarly in my improved system the oscillator tube and its circuit comprise a miniature transmitter, whereas the modulator serves the functions like the microphone above described to modulate the oscillations produced by the oscillator. However, the resultant modulated wave produced by the oscillator instead of being radiated from an aerial, as from a broadcasting station, as in the illustration above given, is caused to pass through a radio frequency amplifier comprising, for example, one or more radio frequency transformers, which amplifies it tremendously, after which it is rectified by the detector tube and the signal is rendered audible. In fact, except for the amplification of the modulated oscillations produced bythe oscillator, my improved system functions essentially like a combination broadcasting and receiving station such as illustrated in Figs. 1 and 2;

In the circuit shown in Fig. 3, the vacuum tube V produces continuous undamped oscillations by its association with the proper circuit including the two coils L L coupled together, the variable condenser K and its filament and plate batteries A and B supplying the power as in the ordinary oscillator arrangement using vacuum tubes. My modulator is connected between points X and X and is composed of another vacuum tube V with its associated circuits. The tuning arrangement, which may be any standard circuit for tuning in the incoming frequency, is, in this case, represented by the antenna N, the coil L and the ground G. 'A variable condenser K is shown in this circuit to vary the wave-length, but any other well known equivalent such as variable inductances or other arrangements may be employed for the purpose. The secondary circuit composed of the coil L and the variablecondenser K is connected directly to the grid and filament of the tube V called by .me the modulator tube. The telephone receivers or recording instrument P is shown connected in the plate circuit across a by-pass capacity K-. The whole system connected between points X and X acts as a variable resistance across the grid-filament path of the vacuum tube V in a manner similar to the arrangement of Fig. 4, in which the resistance R is shown in place of the modulating arrangement, and in which the constants of the circuit are the same as in Fig. 3. If desired, the modulator, tube V may be replaced by any suitablevariable resistance, the value of which may be varied by incoming signals and acting as the vacuum tube V in the circuit of Fig. 3.

The circuit of Fig. 3 operates as follows: Nhen the filament and. plate batteries are connected as shown to the circuit of the vacuumtube V this tube produces oscillations in the circuit L L K, and the frequency of these oscillations may be adjusted by either varying the condenser K or by properly adjusting the value of the two coilsL and L Then this circuit is producing oscillations, points X and X become alternately positive and negative. When point X is at a positive potential as it is during each half oscillation, a current flows through the vacuum tube V since the plate is at a positive potential. But when point X becomes negative during the other half of the oscillation, no current flows since the tube acts as a rectifier or valve and can only function when the plate is positive. During this process, a difierence of potential is set up between X and X since the resistance of the tube is sufliciently high, and a current flows in the telephones P or recording device connected between the tube V and point X. This is illustrated in a simple way in Fig. 5, where the resistance R represents the internal resistance or impedance of the vacuum tube V. In this arrangement there is, therefore, a pulsating current flowing in a circuit connected between points X and X When no signal is received, the pulsating current is always of the same amplitude and intensity and since it is above audibility, nothing is heard or recorded in the telephones or recording device.

When a telegraph or telephone signal is received in the antenna system or collecting agency, an alternating current is set up in circuit L K and impresses between the grid and filament of the vacuum tube V re ferred to herein as the modulator tube, an alternating potential making the grid of this tube alternately positive and negative. During each half cycle when the grid is positive, the resistance of the vacuum tube V decreases and a greater current flows in the circuit connected between the points X and X while on the contrary, when the grid becomes negative, the resistance increases and the currents in the circuit decrease. Since these variations are produced at an inaudible frequency, no signal could be heard in the telephones if these variations of resistance alone were made use of. However, these periodic variations combine with the variations of polarity of the plate of the modulator tube and produce an audible response (beat note) in the telephones P or recording device. T he frequency of the oscillations produced by the oscillating circuit connected to the vacuum tube V may be very high or very low depending upon the results which it is desired to obtain.

Fig. 6 shows'a modification of the circuit of Fig. 3 in that a grid condenser K is connected between the oscillating circuit L K and the grid of the vacuum tube V producing the oscillations. The modulating arrangement connected between points X and X acts as a so-called grid leak and makes clear my improved method of employing a vacuum tube as a variable resistance for the purpose of receiving radio signals. This circuit is merely a variation of the circuit of Fig. 3, which is identical except for the grid condenser K which in practice is not essential, although desirable, for obtaining the best results in the operation of the circuit.

Figs. 7 and 8 show another arrangement of circuits employing my invention of using a vacuum tube as a resistance to modulate a local source of power. in the diagram of Fig. 7 the oscillating circuit is composed of the coil L and the condenser K which is shown variable for the purpose of varying the frequency of the circuit. The fixed condensers K and K are merely stopping condensers to prevent the battery B from being short-circuited and from applying a high positive potential on the grid of the vacuum tube V". As may be seen in this diagram, the modulating arrangement is connected between points X and X as in Fig. 3, and the operation of this circuit is the same as the one previously described except that the arrangement of the system is different. Fig. 8 shows the same circuit as that of Fig. 7, except that in 7 the telephone receivers or recording device are shown connected in the plate circuit of the vacuum tube V producing the local oscillations instead of the plate circuit of vacuum tube V Good results may be obtained from either adjustment, except the former is some times of ad vantage as the variations of potential caused by the modulating arrangement between the points X and X are amplified through the vacuum tube V In all the circuits the letters A and B refer, as is usual, to the filament and plate batteries respectively.

Referring to the construction shown in Fig. 10, the reference letter L designates the primary and L the secondary of a coupler of the modulator circuit, the tuning of which is effected by a variable condenser K which is shunted across the grid input and grid-tofilament return leads of the modulator V A jack J serves to cut in a loop aerial when desired. The oscillator V is provided with a coil L in the grid and grid-to-filament circuit, such circuit being tuned by the variable condenser K. In the plate circuit is interposed a coil L and interposed between these two coils is a stopping condenser K which prevents the flow of the plate or B battery current passing along the lead, which connects to the plate circuit at Z, to the filament of the latter tube V The leads to the primary of the first radio frequency transformer UA, preferably termed herein an ultraformer, is connected between the plate of the modulator tube and the grid of the oscillator tube as indicated by the reference letters X and X respectively, the same being shunted by a small fixed condenser K which is of a predetermined capacity to tune the input circuit to the ultraformer to the particular frequency it is best adapted to amplify efliciently since the ultraformer is preferably adapted to amplify efiiciently at one wave length only.

From the output of the secondary of the ultraformer UA, the current passes through its associated radio frequency amplifier tube V thence to the primary of a second radio frequency transformer U13 and then successively from the secondary thereof through its associated radio frequency tube V to the primary of a third radio frequency transformer UB from its secondary and thence through the grid leak and condenser to the input rid and filament circuit of the detector tube 7 The output circuit of the detector is connected in the usual manner to a jack J of the audio frequency amplifiers and the telephones or loud speaker. Preferably a fixed condenser K is shunted from the plate circuit of the detector tube to the negative lead to the filament or A battery and a potentiometer P is connected across the filament or A battery, the latter serving to accurately regulate or subdivide the voltage.

For the reception of broadcasting programs over a band of wave lengths of from 200- to 600 meters, I have found the following values to give unusually satisfactory results in the super-heterodyne circuit above described:

For each of the two coils L and L to provide acoil preferably 3 inches in diameter and consisting of turns of Number 20 wire; for the coil L a coil preferably 3 inches in diameter and consisting of 8 turns of Number 20 wire; for coil L, a coil'preferably 3 inches in diameter and consisting of turns of Number 20 wire, the said coils L and L being coupled together; for condenser K, a

variable condenser of .001 microfarads; for condenser K preferably a variable condenser of .0005 microfarads; for condenser K preferably a fixed condenser of .001 microfarads; for condenser'K areferabl-y a fixed condenser of .001 microfarads; for condenser K preferably a fixed condenser of .001 microfarads; for condenser K preferably a fixed condenser of .005 microfarads; for condenser K, preferably a fixed conde ser of .00025 microfarads; for transformers UA, UB, UB UB preferably transformers which are all tuned to 3000 meters, wave length; for potentiometer P, any potentiometer suitable for the purpose.

"While I prefer to employ an oscillator tube and its circuit to generate continuous frequency oscillations, I may, if desired, substitute therefor an external source of alternating or interrupted current i. e. intermittent current Which is capable of producing the same results as the oscillator tube and its circuit. The leads of such an external source of an intermittent current can be connected at the points X-X in the figures in lieu of the entire oscillation tube and its circuit.

1 do not limit the application of my invention solely to the circuits shown in the drawing and-described herein; since, as above stated, the system may be modified and the output amplified to obtain greater signal strength, or the circuit may be incorporated into such an arrangement as the superheterodyne receiver in place of the first de- .tecuor and oscillator commonly used in this type of receiving set, and as is obvious other applications may be made of my improved system without departing from the spirit and purpose of my invention.

. What I claim and desire to secure by Letters Patent is:

l. A receiving system for high frequency oscillations comprising a vacuum tube and coupled input and output circuits for causing said tube to act as an oscillator, a second vacuum tube and a tuning circuit therefor adapted to be tuned to incoming high frequency signal oscillations, said second vac uum tube being connected across the input of said first vacuum tube oscillator so as to make the received incoming high frequency oscillations to Which the tuned circuit is tuned affect the internal impedance of the first vacuum tube.

2. An amplifying system for high frequency oscillations comprising an electron tube having an anode, a cathode, a controlling electrode and coupled input and output circuits, a tuning circuit adapted to be tuned to radiated high frequency waves and a second electron tube having its input coupled thereto, said second electron tube having its anode connected to the grid of the firstvacuum tube and having its filament connected to the filament of the first electron tube so as to affect the amplifying action of the first tube when high frequency oscillations are tuned in on the tuning circuit coupled to the second electron tube.

3. A system for receiving electric oscillations composed of a source of energy controlled by a vacuum tube, a second vacuum tube having a tuning circuit connected across its input electrodes, said second vacuum tube having its anode connected to the grid of the first tube thereby varying the amount of energy flowing through the first vacuum tube when oscillations are generated in the tuning circuit of the second vacuum tube.

4:. A system for controlling the amplifying action of a vacuum'tube, comprising a vacuum tube oscillation generator having an input circuit, another vacuum tube connected across said input circuit means for applying to the last mentioned tube desired radio frequency signal energy so as to cause said signal energy to control the internal impedance of said generator by varying the grid voltage of said second tube.

5. A system of varying the amplitude of electric oscillations produced by an electron tube generator, consisting of a vacuum tube generator for generating said oscillations having an input circuit, another electron tube connected across said input circuit, means for causing received radio signals to affect the amplitude of said oscillations by varving the grid voltage of the second tube which is thereby made periodically operative, and means for making audible said radio signals.

6. A Wireless receiving system comprising an electron discharge device having plate and grid circuits, means for impressing received Waves on the grid circuit of said electron discharge device and means independent of said device for producing and impressing on the plate circuit of said device an alternating potential of a frequency diifering from the received frequency by a super-audible frequency.

7. Radio signalling apparatus comprising a generator of high frequency oscillations coupled to the output circuit of an electron discharge device having an anode, a cathode and a control electrode, said output circuit being devoid of a source of constant electromotive force, means for applying across the control electrode and cathode of said electron discharge device high frequency oscillations differing from the generated oscillations by a super-audible frequency, whereby current flows from the cathode to the anode of said electron discharge device only when said anode and control electrode become relative 1y positive with reference to said cathode.

In testimony whereof I have hereunto set my hand this 28th day of April, 1924.

ROBERT E. LACAULT. 

